Microalgae to Biofuel: Cutting-Edge Harvesting and Extraction Methods for Sustainable Energy Solution

Abstract

The increasing price and demand for fossil fuels are driven by their depletion, greenhouse gas emissions, and industrial air pollution. As a result, the search for renewable alternatives has gained serious attention. Microalgae provide a sustainable alternative for biofuel production, offering high growth rates, significant oil yields and productivity, nontoxic nature, higher photosynthesis efficiencies, and the ability to thrive on nonarable land. Chlorella vulgaris and Scenedesmus dimorphus strains were chosen for this study to develop effective harvesting and oil extraction methods for sustainable energy. Three types of harvesting methods are used to optimize slurry yields, viz. flocculation, high-speed refrigerated centrifugation, and microfiltration. Moreover, two oil extraction methods were considered to enhance efficiency: Soxhlet extraction and the direct boiling method. The centrifugation method provides the fastest harvesting rate and highest slurry yields, followed by membrane separation, while flocculation, though slower, is more cost-effective and easier to perform. The direct boiling method optimizes the oil extraction process by effectively rupturing microalgae cell walls. Chlorella vulgaris shows a slurry recovery efficiency of 0.76 g per liter of media by centrifuge, consisting of 12%–40% oil content in overall weight; 12.7% of the oil was extracted using Soxhlet extraction, and 18.7% was extracted using the direct boiling method. On the other hand, Scenedesmus dimorphus shows better slurry recovery efficiency of 0.81 g per liter media by centrifuge, consisting of 22%–51% oil content in overall weight, and there is 23.8% oil extracted by using soxhlet extraction and 26.4% for every 10 g of the sample by direct boiling method compared to Chlorella vulgaris. Future research should focus on cost-effective harvesting and oil extraction methods for microalgae like Chlorella vulgaris and Scenedesmus dimorphus to reduce production costs, maximize biofuel yields, and tackle the global energy crisis.